If michael jackson had lupus, he would have to hide it in order to be able to keep working. that's how show biz works. you can't get anyone to insure your tour if you might end up sick and cancel because of a rpe-existing condition. so if i were him and wanted to keep open the option of working, i would hide the fact that i had lupus. also, lupus is so misunderstood that i imagine he did not want to have to be the poster child for it and have ot educate everyone on this misunderstood disease. he had enough crap swirling around him as it was.
lupus would explain everything- the umbrellas shielding him from the sun, the autoimmune skin disease, the need for pain killers and other drugs. And the cardiac arrest. Most people who die from lupus die of cardiac arrest.
some say that anna nicole smith had lupus, and that she hid it because she didn't want to be remembered that way.
very few celebs come out and admit to a chronic illness. lots of them come out and talk about cancer, because cancer has had a great public campaign of awareness and no stigma attached to it anymore. also, it's something that happens, then you get better. the chronic illness... is chronic.